A known oxy/coal combustion system includes a furnace (or radiant section) arranged and disposed to receive a fuel and oxidant to form a combustion fluid, a convective section arranged and disposed to receive the combustion fluid, and one or more heat exchangers arranged and disposed to transfer heat from the combustion fluid to a heat exchange medium. In steady operation, the known oxy/coal combustion system extracts energy by harnessing the heat in the heat exchange medium.
The known oxy/coal combustion system may be subject to start-up conditions, by way of example only, upon first being constructed, subsequent to being shut down for maintenance, or subsequent to a trip event. The known combustion system may be subject to shut down conditions, by way of example only, prior to scheduled maintenance, in response to a trip event, in response to a decreased availability of fuel, or in response to operational limitations. The known combustion system may be subject to a trip event, by way of example only, upon operational problems such as turbine trip events, in response to forced or induced draft fan trip events, in response to mill issues, in response to a loss of flame conditions, or in response to over-pressuring of one or more sections of the combustion system.
As is well known in the art, combustion of carbonaceous fuels results in of CO2. The emission of CO2 occurs during steady operation, start-up, shut-down, and trip events.
Several known technologies for CO2 capture exist. These known technologies focus on post combustion and/or pre-combustion CO2 capture. For example, at low concentrations or partial pressures, chemical solvents may be used to scrub flue gas. Use of chemical solvents results in energy loss required to regenerate the lean solvent to obtain a high CO2 capture levels. Alternatively, CO2 can be captured prior to combustion utilizing physical sorbents from a integrated gasification combined cycle, IGCC, plant design. This design requires high purity, high pressure oxygen and generates hydrogen gas which is subsequently burned in a gas turbine to produce power. High levels of substantially pure CO2 require non-standard designs for the physical solvent system. A third option is to use lower purity, lower pressure oxygen as the oxidant to combust in a standard utility boiler arrangement. The flue gas from the oxygen-fired option is depleted in nitrogen thus increasing the CO2 partial pressure. The gas can then be cooled, water condensed, and purified to produce a CO2 product.
In known oxy/fuel combustion systems, during start-up, shut-down, and trip events, CO2 is not able to be adequately captured and purified because CO2 levels remain lower than the predetermined level for a longer than desired period.
Therefore, there is an unmet need to provide a method, system, and apparatus improving CO2 capture by increasing and/or maintaining level of CO2 in oxy/fuel combustion systems during start-up, shut-down, and/or trip events.